Total Radiation Pyrometer - Construction, Working, Advantages & Applications

The total radiation pyrometer is a type of pyrometer in which total radiation or total heat emitted from the hot body or temperature source is focused on the radiation sensing element. In this, both visible and invisible radiations are virtually received by the radiation sensing element. Generally, thermocouple, bolometer, or thermopile are used as a radiation sensing element that measures the temperature of the radiations received.

Principle of Total Radiation Pyrometer :

The process of measuring temperature using this type of pyrometer makes use of the total energy emitted by the hot body i.e., uses the intensity of the total radiation emitted.

The energy is then known by 'Stefan Boltzman Law', which states that the total intensity of the emitted radiations from a black object is proportional to the fourth power of the temperature of the hot body i.e., E ∝ T⁴.

The operating principle of this pyrometer is that the total radiation of a hot body whose temperature is required to be known is made to fall on the devices which receive the radiation such as thermocouple, bolometer, thermopile, etc., and the emf developed by these devices gives the temperature of the hot object.

Construction of Total Radiation Pyrometer :

The total radiation pyrometer contains a tube that houses the components of this pyrometer. One end of the tube is open to receive radiations from the temperature source or hot object whose temperature is to be determined, and the other end has a sighting hole (which contains an adjustable eyepiece). The below shows the construction of the total radiation pyrometer.

Inside the tube an adjustable lens (whose position can be adjusted by rack and pinion mechanism to make total radiation fall on the receiving element) and a radiation receiving element (thermocouple) are present. The thermocouple is connected to a millivoltmeter which is calibrated in terms of temperature.

Working of Total Radiation Pyrometer :

As shown in the figure the temperature source emits radiation. All the emitted radiation is focused on the hot junction of the thermocouple through the lens.

When the thermocouple receives the radiation, a temperature difference occurs in it and a proportionate emf will be generated which can be indicated and read by the millivoltmeter, which in turn indicates the temperature of the source of the hot object.

Advantages of Total Radiation Pyrometer :

• It can be used to measure a high range of temperatures.
• It can measure the temperatures of those objects which are fixed at someplace and also the objects which are moving.
• It is a non-contact type of pyrometers i.e., they measure the temperature of hot objects without contacting them.
• It produces a fast response.

Disadvantages of Total Radiation Pyrometer :

• Exhibits poor performance if any dust particles or gases are present between the hot object and the receiving lens.
• Sometimes it requires some cooling arrangement to remove the overheating of the instrument.
• There is a problem in focusing the total radiation on the thermocouple if the lens is not placed properly.
• It cannot be used to measure low temperatures.
• It is expensive.

Applications of Total Radiation Pyrometer :

• It is used to measure temperatures in a bright annealing furnace, hydrogen atmosphere in copper bearings.
• It is used to measure the temperature of hot objects within a furnace.
• It is used in conditions where thermocouples fail to operate.